The present invention relates to an automatic screen-cleaning apparatus. In particular, the present invention relates to an automatic screen cleaning apparatus for use as part of a sewage pumping station or the like.
Sewage pumping stations are conventionally underground structures that foul or surface water sewage is discharged into There are various types of sewage stations, but in smaller systems the sewage station is typically a wet well i.e. where the pumping station houses one or more submersible pumps which pump the sewage onwards to its next destination. In a larger station there may be a separate dry well, adjacent to the wet well, which houses the pumps. Alternatively, on some pumping stations the pumps may be housed above ground near the wet well.
In storm conditions or other extreme circumstances which would be sufficient to flood the pumping station with sewage in volumes which exceed the intended capacity of the sewage pumping station, many pumping stations have consent to discharge sewage in a controlled manner into a nearby river or stream. Such consent is issued by the Environmental Agency in an effort to avoid a breach of raw sewage at ground level where the pumping station is situated. In the event of such an extreme situation arising, sewage is discharged from the pumping station via an outfall' into a nearby river or stream.
The most common causes of flooding of pumping stations include heavy rainfall, electrical power failure, for example caused by power-cuts, mechanical breakdown of pumps, and downstream blockage of the sewage transit pipe system.
Most pumping stations are required to filter the sewage to prevent larger particles of sewage solids or Rag being discharged. Rag is the generic name for any non-organic material that is present in the sewage liquid and includes materials such as toilet tissue, old dish cloths and other fabric materials, and other items that may be found floating on the top of the sewage surface.
If the screen becomes blocked, less filtered sewage is discharged and thus, if more sewage is entering the pumping station that is able to be discharged through the blocked or partially blocked screen, the sewage level at the pumping station rises and eventually the sewage will breach the ground surface, rather than being safely discharged into a nearby river or stream. As some pumping stations are located in residential areas, this is both unhygienic and undesirable.
One prior art solution that attempts to address this problem involves a high pressure jet arrangement located so as to spray the residue or rag off the screen in a cleaning action, thereby keeping the screen in an unblocked state. Such systems may be automated when used in combination with a sonar device, but have expensive installation and operating costs. For most pumping stations the cost of automated screen cleaning is not economical, and so the screen is cleaned manually using a rake or a mobile pressure washer when an operator visits the site. The manual cleaning is normally triggered after a storm event, but this operation is often missed and the screen remains at least partially blocked.
There is therefore a need for a low cost way to facilitate efficient automated screen cleaning.